A prospective study was carried out on 747 infants: 147 neurologically abnormal, 300 with mild neurological abnormalities and 300 normal infants. They were re-examined at nine years of age, with special attention being paid to minor neurological dysfunction (MND). Extensive data on obstetrical history, neonatal course and interval complications were collected. Neurological handicap was not found on follow-up in the group of normal newborns. Other than neonatal neurological abnormality, risk factors contributing significantly to later handicap were low one-minute Apgar scores, a disturbed neonatal course, low social-class and interval complications; obstetrical events were conspicuous by their absence. Two aetiologically and clinically distinct kinds of MND were distinguished on the basis of a neurological cluster profile: MND-1 (one or two abnormal clusters) was only associated with a birthweight below the 2.3 centile and male gender, and MND-2 (more than two abnormal clusters) was associated with neonatal neurological findings, social class, obstetrical optimality score and gender.